Current communication systems use a symmetric key-based authentication and key agreement (hereinafter referred to as “AKA”) method as a user authentication and key exchange method. However, in the case of using the symmetric key-based AKA method, a user identifier (hereinafter referred to as “ID”) is exposed, and thus user tracking becomes possible.
Recently, research for solving the problem caused by the use of the symmetric key-based AKA method (i.e., the problem that the user ID is exposed and user tracking becomes possible through the use of a public key-based AKA method) has been actively performed.
Also, in the case of using the symmetric key-based AKA method, the amount of computation that is performed in a user's universal subscriber identity module (hereinafter referred to as “USIM”) is increased. That is, the amount of computation required for the symmetric key-based AKA method is much greater than the amount of computation required for the public key-based AKA method. Accordingly, in the case where the symmetric key-based AKA method is used in a USIM that is restricted in the amount of computation, it is difficult to process the required amount of computation.